The present invention relates generally to electric motors and more specifically to an electronic control system for a brushless DC motor.
DC brushless motors are often used in servo control systems in a wide variety of applications. Typically, brushless motors are constructed with stationary windings and a rotary permanent magnet field. The windings are commutated by solid state switches controlled in response to signals from rotor position sensors. Since the brushes and commutator of the normal DC motor are eliminated, and since commutation is controlled by solid state switches, brushless motors require sophisticated electronic motor control systems. A representative example of a brushless DC motor having an electronic control system is disclosed in U.S. Pat. No. 4,368,411, entitled "Control System for Electric Motor," issued Jan. 11, 1983, by H. Keith Kidd.
Electronic control systems for brushless DC motors typically include a plurality of sensors for sensing the relative position of the permanently magnetized rotor relative to the stator windings. The position sensors usually comprise Hall sensors and magnets, photo interrupters and a shutter wheel, or some other similar arrangement. The position sensors provide output signals which are used to control switches in a bridge circuit in order to apply current to the stator windings in an appropriate sequence. If the position sensors malfunction, the switches can apply excessive currents to the stator windings thereby causing damage to the motor.
It is an object of the present invention to provide an electronic control system which can detect errors in the output signals of the position sensors of a brushless DC motor.
It is another object of the present invention to provide an electronic control system which can shut off the brushless DC electric motor once error signals have been detected.